The invention relates to binaural hearing aids, and more specifically relates to small binaural hearing aids. In its most immediate sense, the invention relates to binaural CIC and ITE aids, i.e. hearing aids which are worn Completely In the Canal of the patient's ear or In The Ear of the patient.
Conventional hearing aids have only one microphone, and that microphone is generally of a nondirectional type (so the patient can hear sound from any direction relative to the patient's head). This nondirectionality impairs the patient's ability to determine the direction from which a sound originates. This can cause difficulties for the patient. For example, when a patient is addressed by another person and seeks to face the speaker, the patient may turn in the wrong direction. Similarly, if a patient hears a directive to e.g. move out of the way of danger, the patient may move in the wrong direction and toward the danger. For these reasons, binaural hearing aids have been developed.
A binaural hearing aid is an aid having two or more microphones. When a sound is detected by more than one microphone, the outputs of the microphones will almost always be different because the microphones will only seldom be precisely equidistant from the sound source. As a result, the directionality of the sound produces changes in the electrical signals from the microphones. By appropriate design of the hearing aid circuit, these changes can be used to vary the audio output from the hearing aid, thereby making it possible for the patient to assess, at least approximately, the direction from which a sound originates.
As a practical matter, a binaural hearing aid cannot provide useful information unless the microphones are sufficiently spaced apart. At a minimum, the microphones must be 12 mm apart. Such a spacing is very difficult to achieve with a CIC aid and with certain ITE aids.
A CIC aid is very tiny because it is worn deep within the patient's ear so as to be inconspicuous and indeed almost invisible. The small size of a CIC aid makes it difficult to provide a CIC aid with binaural capability.
This difficulty comes about because a conventional single-microphone CIC aid has the microphone ported through the faceplate. If a conventional CIC aid design is modified to provide two microphones ported through the faceplate, the faceplate must be enlarged. Such an enlargement makes the aid less marketable, because fewer patients have ear canals that are sufficiently large to accommodate the aid. Furthermore, adding an additional microphone to the faceplate of a conventional CIC design increases the risk of feedback. This is because faceplate space is limited, and when an additional microphone is added to the faceplate, one or both of the microphones may be well coupled to the receiver. An ITE aid, while being larger than a CIC aid, is also relatively small and is subject to the same problems (although the problems are somewhat less severe).
It would be advantageous to provide a binaural hearing aid having the cosmetic advantages of a CIC aid or a small ITE aid without being unduly large. And it would also be advantageous to provide a binaural CIC or ITE hearing aid that would not be unduly subject to feedback.
The invention proceeds from the realization that the retrieval line that is always provided on a CIC aid can support an additional microphone to thereby produce a binaural hearing aid. A retrieval line is a thin filament of e.g. skin-colored plastic that is fixed to the hearing aid housing and that is sufficiently long to extend out of the patients ear canal. A retrieval line may be, and conventionally is, enlarged at its distal end to make it more easily graspable.
In accordance with the invention, a binaural hearing aid is provided. The aid has a housing; the housing has a faceplate and contains a hearing aid circuit. An elongated flexible line is provided. The line has a proximal end fixed to said housing and a distal end remote from said housing, and the line extends from the housing in such a manner that a patient wearing the hearing aid in an ear can grasp the line and can pull the hearing aid out of the ear by pulling on the line.
A first microphone is located within the housing. The first microphone is operatively connected to the hearing aid circuit and is ported through the faceplate. A second microphone is also provided. The second microphone is operatively connected to the hearing aid circuit and is fixed to the distal end of the line.
Because the second microphone is located at the distal end of the line, it occupies no additional space on the faceplate. Consequently, the overall size of the faceplate (and therefore of the aid) need not be increased. Furthermore, the coupling between the microphones and the receiver is substantially less than it would be if both microphones were ported through the faceplate. This reduction in coupling makes the aid less subject to feedback.
When the distal end of the line is enlarged, this makes it easier for arthritic and nondexterous patients to grasp the end of the cable.